How do I flush the cin buffer?

How do I clear the cin buffer in C++?

I would prefer the C++ size constraints over the C versions:

// Ignore to the end of file
std::cin.ignore(std::numeric_limits<std::streamsize>::max())

// Ignore to the end of line
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n')

Possibly:

std::cin.ignore(INT_MAX);

This would read in and ignore everything until EOF. (you can also supply a second argument which is the character to read until (ex: '\n' to ignore a single line).

Also: You probably want to do a: std::cin.clear(); before this too to reset the stream state.

cin.clear();
fflush(stdin);

This was the only thing that worked for me when reading from console. In every other case it would either read indefinitely due to lack of \n, or something would remain in the buffer.

EDIT: I found out that the previous solution made things worse. THIS one however, works:

cin.getline(temp, STRLEN);
if (cin.fail()) {
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

I have found two solutions to this.

The first, and simplest, is to use std::getline() for example:

std::getline(std::cin, yourString);

... that will discard the input stream when it gets to a new-line. Read more about this function here.

Another option that directly discards the stream is this...

#include <limits>
// Possibly some other code here
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');

Good luck!

int i;
  cout << "Please enter an integer value: ";

  // cin >> i; leaves '\n' among possible other junk in the buffer. 
  // '\n' also happens to be the default delim character for getline() below.
  cin >> i; 
  if (cin.fail()) 
  {
    cout << "\ncin failed - substituting: i=1;\n\n";
    i = 1;
  }
  cin.clear(); cin.ignore(INT_MAX,'\n'); 

  cout << "The value you entered is: " << i << " and its double is " << i*2 << ".\n\n";

  string myString;
  cout << "What's your full name? (spaces inclded) \n";
  getline (cin, myString);
  cout << "\nHello '" << myString << "'.\n\n\n";

How about:

cin.ignore(cin.rdbuf()->in_avail());

I prefer:

cin.clear();
fflush(stdin);

There's an example where cin.ignore just doesn't cut it, but I can't think of it at the moment. It was a while ago when I needed to use it (with Mingw).

However, fflush(stdin) is undefined behavior according to the standard. fflush() is only meant for output streams. fflush(stdin) only seems to work as expected on Windows (with GCC and MS compilers at least) as an extension to the C standard.

So, if you use it, your code isn't going to be portable.

See <https://stackoverflow.com/questions/2979209/using-fflushstdin>;.

Also, see <http://ubuntuforums.org/showpost.php?s=9129c7bd6e5c8fd67eb332126b59b54c&p=452568&postcount=1> for an alternative.

Another possible (manual) solution is

cin.clear();
while (cin.get() != '\n') 
{
    continue;
}

I cannot use fflush or cin.flush() with CLion so this came handy.

Easiest way:

cin.seekg(0,ios::end);
cin.clear();

It just positions the cin pointer at the end of the stdin stream and cin.clear() clears all error flags such as the EOF flag.

It worked for me. I have used for loop with getline().

cin.ignore()

The following should work:

cin.flush();

On some systems it's not available and then you can use:

cin.ignore(INT_MAX);

#include <stdio_ext.h>

and then use function

__fpurge(stdin)

cin.get() seems to flush it automatically oddly enough (probably not preferred though, since this is confusing and probably temperamental).

fflush(stdin) − It is used to clear the input buffer memory. It is recommended to use before writing scanf statement.

fflush(stdout) − It is used for clearing the output buffer memory. It is recommended to use before printf statement. The following should work:

cin.flush(); On some systems it's not available and then you can use:

cin.ignore(INT_MAX); Both Windows and Linux define the behaviour of fflush() on an input stream, and even define it the same way (miracle of miracles). The POSIX, C and C++ standards for fflush() do not define the behaviour, but none of them prevent a system from defining it. If you're coding for maximum portability, avoid fflush(stdin); if you're coding for platforms that define the behaviour, use it — but be aware that it is not portable portable code does not use fflush(stdin). Code that is tied to Microsoft's platform may use it and it may work as expected, but beware of the portability issues.